This invention relates in general to wheelchairs and to a rotary adjustment mechanism for wheelchair components. More particularly, the invention relates to a mechanism for releasably locking two relatively rotatable members for adjusting the positioning of a wheelchair footrest or other components.
Wheelchairs generally include a frame that supports a pair of drive wheels and a pair of front casters. The drive wheels make contact with the ground and are driven to propel the wheelchair. The drive wheels may be driven manually or powered by an electrical motor. The wheelchair frame also supports a seat assembly comprising a seat and a backrest. The seat assembly is oriented above and between the drive wheels and the front casters to provide stability. Generally, a pair of rigid frame extensions extend off the frame relatively forward from the front casters. Paired foot supports, is consisting of a foot support arm and a foot support plate, are connected to the rigid frame extensions.
Typically, each foot support is joined to its corresponding frame extension using an adjustable mechanism to permit the angle of each foot support to be easily adjusted to meet the specific needs of the user. For example, if the wheelchair user has a leg or foot fracture or other injury in one leg, the foot support can be adjusted to position the affected limb parallel to the ground.
An adjustable locking mechanism is described in U.S. Pat. No. 5,689,999, titled Adjustable Rotary Locking and Unlocking Apparatus. This locking mechanism consists of two members rotatably connected by a bolt through a central bore. A first member has a plurality of arcuately spaced locking pins that are movable between a projected and a retracted position. A second member has a plurality of arcuately spaced sockets configured so that each socket can accommodate any of the locking pins. To reposition the foot support, the user pushes an actuator to retract all the locking pins into the second member thereby permitting the first member and the second member to rotate freely relative to each other.
Any mechanism for adjusting the angle of the foot support must be solidly constructed because the foot support arm acts as a lever arm to concentrate pressure placed on the foot support plate. In the rotary locking apparatus described in the '999 patent, pressure on the footplate is focused on the bolt. The '999 patent describes careful fabrication to provide a snug fit between the locking pins and the sockets and the supporting bolt and the central bore. Unfortunately, this increases cost without a proportional increase in the overall strength of the mechanism.
Thus, it would be desirable to have an improved adjustable rotary positioning mechanism of increased strength that can be inexpensively fabricated.